Any unilateral step by Ethiopia to fill its hydropower project, called the Renaissance Dam, in July would directly threaten Sudan's national security, Sudanese Irrigation and Water Resources Minister Yasser Abbas said on Saturday.

Sudan is also proposing a mediation role for the United States, European Union, United Nations and African Union as a way of breaking the deadlock in talks about the dam between Sudan, Egypt and Ethiopia, Abbas told Reuters in an interview.

His comments come at a time of increased tension between Sudan and Ethiopia over disputed farmland near their shared border.

This is on top of tension over the Grand Ethiopian Renaissance Dam (GERD), which Ethiopia is building on the Blue Nile, close to the border with Sudan.

Ethiopia began filling the reservoir behind the dam after the summer rains last year despite demands from Egypt and Sudan that it should first reach a binding agreement on the dam's operation.

Egypt views the Grand Ethiopian Renaissance Dam as a major threat to its fresh water supplies, more than 90% of which come from the Nile. The Blue Nile flows north into Sudan then Egypt and is the Nile's main tributary.

Ethiopia says the dam is crucial to its economic development.

"The filling of the Renaissance Dam by one side next July represents a direct threat to Sudan's national security," said Abbas.

He said unilateral filling of the reservoir threatened electricity generation from Sudan's Merowe Dam and Roseires Dam, as well as the safety of the Roseires Dam and of 20 million Sudanese living downstream of the GERD.

Sudanese drinking water stations could also be put at risk, he added.

The African Union has convened recent negotiations over the GERD between Ethiopia, Sudan and Egypt but talks have repeatedly stalled. Talks hosted by the United States last year also failed to secure a deal.

"Sudan is now leading a diplomatic and political campaign to clarify its position and reach a legal and binding solution," Abbas said.

"We are optimistic that if there is political will, a mutually agreed solution can be reached."